This invention relates to a body for a disc brake caliper for motor vehicles and to a disc brake caliper comprising such a body.
In a typical disc brake, a brake caliper straddles the outer peripheral margin of a brake disc. The brake caliper usually has two limbs and is arranged so that the limbs overly opposite sides of the brake disc. Friction pads are received between each limb of the caliper and the brake disc and at least one of the limbs has one or more hydraulic piston and cylinder assemblies therein for applying the friction pads to the disc.
Known calipers are of two basic types, moving calipers and fixed calipers. In a moving type caliper, the limbs are movably connected to one another. One or more hydraulic piston and cylinder assemblies are located in a limb on one side of the disc for direct application of friction pad(s) on that side of the disc, the friction pad(s) on the other side of the disc being applied by the reaction movement of the other limb. In contrast, in a fixed caliper the limbs are rigidly interconnected at either end by a bridging member that spans the radial edge of the disc and each limb has one or more hydraulic piston and cylinder assemblies for direct application of the friction pads to their respective side of the disc.
Known disc brake calipers are usually secured to a support structure of the vehicle that is fixed relative to the brake disc, such as a stub axle or the forks of a motorcycle for example. In a typical arrangement, one of the limbs has two or more mounting portions, each having a fastener hole for receiving a fastener, such as a bolt, for mounting the caliper to the support structure.
A typical brake caliper comprises a body which includes the limbs and, in the case of a fixed caliper, the bridging members. Various components such as the pistons and seals are mounted to the body. Usually the body is manufactured from a metal such as aluminium, aluminium alloy or steel. The body may be formed as a casting which is machine finished or it may be machined from one or more solid pieces of metal or billets. Where the body is machined from billet, the billets may be rolled or they may be a forging.
In a moving type caliper, the two limbs are manufactured separately and interconnected by means of pins or the like so that the reacting limb can move relative to the fixed limb.
In the case of a fixed caliper, the body can be produced in two parts, each part typically comprising one of the limbs and part of each the bridging members. During manufacture, the parts are assembled together using bolts or other fastenings to form the caliper body. Alternatively, it is also known to produce a fixed caliper body in one piece. This latter arrangement is often referred to as a mono-bloc construction.
FIG. 1 shows the body 10 of a known fixed type brake caliper. The body 10 is of mono-bloc construction and comprises two limbs 11, 12 interconnected at either end by a spaced bridging member 13, 14. Stiffening struts 15, 16 extend at right angles to one another between the two limbs 11, 12 and the two bridging members 13, 14 respectively. The body 10 is designed to sit over the periphery of a brake disc (not shown) in a known manner with the limbs overlying opposing side faces of the disc. Three cylinders 17 are formed in each limb for receiving hydraulic pistons (not shown). In use, the pistons are moved inwardly towards the brake disc to press disc brake pads (not shown) into contact with opposing sides of the disc in a known manner. One of the limbs 11 has a pair of mounting holes 18 by means of which the caliper can be mounted to a fixed support.
When the brakes are applied, the clamping force applied by the disc pads to the disc is reacted by the body and results in the limbs 11, 12 being deflected outwardly away from the disc. This can result in an increased travel of the pistons and hence increased travel of the brake pedal. The caliper body 10 must have sufficient structural rigidity that these deflections are kept within acceptable tolerances. However, there is also a need to keep the weight of the caliper to a minimum. This is particularly so where the caliper is to be used on a high performance vehicle in which weight considerations are of great importance and where the braking forces are particularly high.
There is a need, therefore, for an improved disc brake caliper body which has increased structural rigidity or which can provide equivalent structural rigidity to that of conventional caliper bodies but using less material.
There is also a need for an improved disc brake caliper having such a body.
In known caliper bodies, the cylinders are located in a housing which forms part of the limb, such as the housings 20 on the body 10 shown in FIG. 1. Usually a lateral outer face 21 of the housing extends substantially perpendicularly to the axis of the cylinders and hence parallel to the friction surfaces of the disc in use. To save weight, the radially outer and inner faces (the upper and lower faces as shown) 22, 23 of the housing are sometimes machined to match the profile of the cylinders where this can be achieved without compromising the structural rigidity of the caliper. Where the upper and lower faces 22, 23 of the housing are machined in this way, the regions of the housing 24 surrounding the side walls of each cylinder extend generally parallel to the axis of the cylinder, except at the lateral inner and outer edges where they are radiused.
The known arrangements provide for a rigid structure whilst attempting to reduce the weight of the caliper body. However, there is a need for a caliper body having cylinder housings that provide increased rigidity or which can provide equivalent levels of rigidity with less material. There is also a need for an improved disc brake caliper having such a body.